The invention relates to a threshold selection circuit suitable for a processing unit for the processing of video signals obtained from an angle tracking device, such as a television angle tracking device.
Only video signals which exceed a given threshold, derived from a threshold selection circuit, are selected for application to the processing unit; optimal results are thereby obtained if the threshold level is set just above the black level of the video signals supplied.
Such a threshold selection circuit is commonly known and may, for example, consist of a manually adjustable resistance divider circuit. Further it may comprise a manually controlled stepping switch to select the threshold from a number of discrete voltage levels.
A disadvantage of such a selection circuit is that the threshold selection occurs manually, encumbering the acquisition of optimal results. This disadvantage is particularly felt when, through an abrupt jump in the average intensity level of the video signals, a rapid adjustment of the threshold level is required.